Financial stocks are among the worst-performers in the S&P 500 SPX on Tuesday, after more than one fresh challenge in the sector. FDIC Chairman Martin Gruenberg said large regional banks should face new rules and tougher oversight. Fitch analyst Chris Wolfe said the debt rating agency may be forced to downgrade many U.S. banks after a ratings watch it posted in June. If Fitch downgrades the industry by one notch to AA- from A+ it would have to reevaluate ratings on more than 70 U.S. banks it covers, Wolfe said in an interview with CNBC-TV. In a third development, Discover Financial Services DFS fell 9% as the worst performer…
